[Builder] CSS work

[Christian Hergert <christian hergert me>]

Is anyone interested in helping with CSS work on Builder's UI? We have a
bunch of mockups that need to be implemented in Builder. Most of them
can be done by adding a class here or there to some widgets. But
additionally it just is going to take some time and love.

I'd do it, but LibIDE is clearly my priority at the moment. I have some
quick examples to get things going for whoever wants the challenge.

-- Christian